Lookup field without field saving

I am wondering, if there is a solution for the following lookup issue without programming.

I have a main table "marina", assigning a city (FKcity) to the marina. The city is assigned to a country.



Listing the marinas, I join the tables "marina", "city" and "country".



Now comes the problem. When adding or editing a marina, I would like to be able to select the country first, in order to only have the cities of this country to choose for assigning to the marina.
But if I also use the country-field of the original query, PHPrunner says, that it can't save this field. Of course, as this field is not part of the "marina"-table.

This is how I would like to look the form like:


This way, it works fine, but I have no country-field to preselect the cities.


I am aware that having a "FKcountry"-field in the "marina"-table would help. But this would not be nice in terms of normalization. I hope, there is a way to realize this without programming...
Thanks for your help to a newbie in PHPrunner with no PHP programming knowhow (coming from Access-VBA-World).
Oliver